I KNOW it's not diy but ...

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... somebody will know about this.
Spouse gave me a personal DAB radio.
If I listen to it at the same time as I listen to a normal wireless set the DAB sound is 1 - 2 seconds after the other signal.
This even applies to the Greenwich time signal.
Is this normal?
Mary
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I don't have one, but I would think it is normal...
DAB is digital radio, it uses mpeg compression (as far as I am aware) the audio is compressed on the fly then transmitted - in order to transmit the frames, information about the next frame is needed - this is why there is a delay
It is the same on cable TV, there is a short delay compared to terrestrial analogue TV
Sparks...
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We are not talking satellite transmitted digital radio here; are we? If terrestial DAB I guess it takes time to 'pack it' and send? :-) Seasons greetings Mary.
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Nearly. DAB is satellite distributed so there will inevitably be a delay. Nothing to do with it being digital.
--
Woody

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No.
No it isn't.

Yes, it is. It's *entirely* to do with it being digital.

No they aren't.
--
"The road to Paradise is through Intercourse."
[email me at huge [at] huge [dot] org [dot] uk]
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I'm pretty certain DAB is line fed, since the landline structure exists to all the transmitters. Delay is intrinsic with any codec. IIRC, the only satellite fed terrestrial system is CH5.
--
*He who dies with the most toys is, nonetheless, dead.

Dave Plowman snipped-for-privacy@argonet.co.uk London SW 12
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miles high, giving a round trip if 50,000 miles.
at propagation speed, around 186,000 miles per second, that only puts in about a quarter of a second of the delay, so much more of it is due to processing
mike r
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On Sat, 27 Dec 2003 19:38:35 UTC, mike ring

Assuming transmitter and receiver are both vertically below the satellite, or nearly so....
--
Bob Eager
rde at tavi.co.uk
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At Northern Europe latitudes (assuming uplink and reception) about 600mS is usually considered to be the round trip time allowing for various modulation, demodulation and other comms equipment.
The additional delays are as a result of the MPEG1 layer 2 compression and the various forms of error correction and other processing employed in the transmission path.
.andy
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Oh, I accept that...just making an observation!
--
Bob Eager
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However, given the diameter of the earth at roughly 4000 miles, and allowing tangential sight (to give me a right angle triangle, it's 50 years since school) it couldn't be as much a 27000, which wouldn't add much,
My point, which my brain wishes it hadn't tried to show off with, was that all the processing causes most of the lag - now I need a bevvy and a lie down
mike r
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On Sat, 27 Dec 2003 23:03:32 +0000 (UTC), mike ring

Err, I thought the earth was about 8000 miles diameter?
My mathematics is a bit on the rusty side now, but Australia is about 12,000 miles around the surface, so mother earth is about 24000 circumference.
As circumference = PI x diameter then circumference / PI = diameter, which is 24000 / 3.14, approx 8000.
Professor PoP
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wrote:

of a right angled triangle with the height of the satellite "adjusted" to 24000 miles so I could divide through by 4000 to get a
6+1 hypotenuse, 1, Root(7squared - 1) triangle, to give a
4000 x root48 possible height, but it must be less than that as it would require a horizontally aligned dish.
I'm glad you were awake at the back there, just testing ;-)
mike r
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On Sun, 28 Dec 2003 20:35:47 +0000 (UTC), mike ring

Credit where credit is due - it was my intelligent auto-responder ;)
PoP
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the earth is slowing down and getting out of sync with the atomic time standard.
--
geoff

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On Sat, 27 Dec 2003 09:21:27 -0000, Woody wrote:

The satellite delay is probably the largest single delay in the chain but there will coding/decoding/propergation(*) delays as well. The cumulative effect of all those may well be more than the single hop sat delay of about 525mS.
(*) Time it takes the signal to pass through a single bit of kit, frequently with digital kit this will be at least one "frame" in duration.
--
Cheers snipped-for-privacy@howhill.com
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On Sat, 27 Dec 2003 11:45:08 +0000 (GMT), "Dave Liquorice"

There was discussion at one point of putting a deliberate digital delay into the feeds for analogue transmissions as well so that the various services were equalised, and then to have the time signal early so that at the user's receiver the time would be right to at least within about 100mS.
As I understood it, this gets quite complicated because some analogue transmitters are landline fed with satellite as backup so it becomes pretty complex and expensive to implement.
Streaming transmissions over the public internet can incur even longer delays - tens of seconds - because of the buffering that has to be used to cope with the lack of QoS (quality of service) mechanisms to deal with latency and jitter.
.andy
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On Sat, 27 Dec 2003 13:09:30 +0000, Andy Hall wrote:

Running the entire operation early was thought about at one point, but then it was realised that some delays are variable in real time.

Operational nightmare, they find it hard enough not to talk over the pips ATM let alone if they were happening early!

Another reason.

Which leads to the question of how far in advance do you run the network? 1s, 5s, a minute?
--
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wrote:

An interesting post which I shan't remember - except for the expression I was looking for regarding 'regular' transmissions: analogue.
Thanks, Andy.
Mary

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